Adjusting thickness deviation of Dalian film blowing unit

Accurate Adjustment Strategies for Thickness Deviation of Dalian Film Blowing Units

Thickness deviation of films produced by film blowing units is one of the core issues restricting product quality, directly affecting the mechanical properties, barrier properties and subsequent processing applicability of films. As an important industrial cluster for plastic machinery manufacturing in China, Dalian-produced film blowing units are renowned for their stable structure and high control precision. However, to achieve accurate control of film thickness deviation, systematic optimization is still required from multiple dimensions including process parameters, equipment adjustment and intelligent monitoring. Based on the technical characteristics of Dalian-made units, this paper discusses accurate methods for adjusting thickness deviation.

1. Core Causes of Thickness Deviation

Uneven film thickness originates from non-uniform melt flow and tension fluctuations during subsequent cooling and traction, mainly including:

- Extrusion system fluctuations: uneven barrel temperature and unstable screw speed causing melt pressure changes, leading to film thickness fluctuations;

- Improper die head adjustment: asymmetric die lip clearance and uneven die head temperature distribution, resulting in local differences in melt output;

- Cooling system imbalance: uneven air ring air velocity and fluctuating cooling water temperature, causing inconsistent film shrinkage;

- Mismatched traction and winding: fluctuating traction speed and unstable winding tension, leading to film tensile deformation;

- Raw material property fluctuations: changes in melt index (MI), excessive impurities or moisture in raw materials, affecting melt fluidity.

2. Key Technical Methods for Accurate Adjustment

2.1 Precise Control of Extrusion System

Dalian units are generally equipped with segmented temperature control systems and variable-frequency screw drives, with key focuses on:

- Temperature calibration: regularly calibrate thermocouples of barrels and die heads to ensure temperature error ≤±1℃ for each section, especially uniform die head temperature (temperature difference ≤2℃), avoiding local overheating that causes melt degradation or fluidity differences;

- Stable screw speed: adopt closed-loop variable-frequency control to keep screw speed fluctuation ≤±0.5rpm, adjust speed according to raw material MI value to ensure stable melt pressure (fluctuation range ≤0.5MPa).

2.2 Accurate Adjustment of Die Head

The die head is the core component controlling film thickness, and most Dalian unit die heads adopt adjustable structures:

- Die lip clearance adjustment: for manual die heads, symmetrically adjust die lip bolts (adjustment amount 0.01–0.05mm each time) and gradually correct based on offline thickness measurement data; for automatic die heads (e.g., intelligent die heads from Dalian manufacturers), PLC systems receive online thickness data to automatically adjust die lip clearance with response time ≤1 second and deviation controlled within ±3%;

- Die head cleaning and maintenance: regularly clean die lip deposits (every 8–12 hours) to avoid uneven extrusion caused by accumulated materials.

2.3 Optimization of Cooling System

The cooling system directly affects film setting effect:

- Air ring adjustment: most Dalian unit air rings are double-layer adjustable; adjust concentricity between air ring and die head (deviation ≤0.5mm) and control uniform annular air velocity via air dampers (air velocity difference ≤0.2m/s); for multi-layer co-extruded films, match cooling rates of each layer to avoid interlayer delamination;

- Cooling water temperature control: maintain cooling water temperature at 15–25℃ with a constant-temperature water tank, water temperature fluctuation ≤±1℃.

2.4 Coordinated Control of Traction and Winding

Matching traction and winding speeds is critical to avoid uneven stretching:

- Stable traction speed: adopt servo traction system with speed fluctuation ≤±0.1m/min to ensure constant ratio between traction speed and extrusion speed;

- Winding tension adjustment: monitor winding tension in real time via tension sensors, keep tension fluctuation ≤±5N, avoiding excessive tension causing film thinning or insufficient tension leading to loose winding.

2.5 Intelligent Monitoring and Feedback Adjustment

Dalian units often integrate online thickness measurement systems (e.g., beta-ray or infrared thickness gauges):

- Regular gauge calibration: calibrate thickness gauges monthly to ensure measurement error ≤±1μm;

- Closed-loop feedback control: transmit thickness measurement data to the control system in real time, automatically adjust die lip clearance or screw speed to dynamically correct thickness deviation.

2.6 Stable Control of Raw Materials

- Raw material pretreatment: dry raw materials to moisture content ≤0.1%, recycled material ratio ≤30% to prevent impurities from affecting melt fluidity;

- MI value monitoring: test MI value for each batch of raw materials, adjust extrusion temperature or screw speed when deviation exceeds ±0.5g/10min.

3. Daily Maintenance Safeguards

Daily maintenance is fundamental to maintaining precision besides process adjustment:

- Equipment cleaning: clean screws, barrels and die heads weekly to prevent carbonization of accumulated materials;

- Component inspection: check wear of heating rings, sensors and transmission parts monthly, replace damaged parts promptly;

- Parameter recording: establish a production parameter database, analyze deviation rules and optimize process schemes.

Conclusion

Thickness deviation adjustment of Dalian film blowing units requires integration of equipment characteristics and process optimization. By precisely controlling extrusion, die head, cooling and other processes, assisted by intelligent monitoring and feedback systems, film thickness deviation can be controlled within ±2%. Operators must master equipment principles and adjustment skills combined with daily maintenance to continuously produce high-quality films and enhance enterprise competitiveness.